package com.history.common;

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Random;

import org.apache.log4j.Logger;

public class RandomHelper {
    private static Logger logger = Logger.getLogger(RandomHelper.class);

    private static Random random;
    private static SecureRandom secureRandom;
    private static String id;
    private String valueBeforeMD5 = "";
    private String valueAfterMD5 = "";

    /*
     * Static block to take care of one time secureRandom seed. It takes a few
     * seconds to initialize SecureRandom. You might want to consider removing
     * this static block or replacing it with a "time since first loaded" seed
     * to reduce this time. This block will run only once per JVM instance.
     */
    static {
        secureRandom = new SecureRandom();
        long secureInitializer = secureRandom.nextLong();
        random = new Random(secureInitializer);
        try {
            id = InetAddress.getLocalHost().toString();
        } catch (UnknownHostException e) {
            logger.debug("Error:" + e);
        }

    }

    /**
     * Default constructor. With no specification of security option, this
     * constructor defaults to lower security, high performance.
     */
    public RandomHelper() {
        getRandomGuid(false);
    }

    /**
     * Constructor with security option. Setting secure true enables each random
     * number generated to be cryptographically strong. Secure false defaults to
     * the standard Random function seeded with a single cryptographically
     * strong random number.
     */
    public RandomHelper(boolean secure) {
        getRandomGuid(secure);
    }

    /**
     * Method to generate the random GUID
     */
    private void getRandomGuid(boolean secure) {
        MessageDigest md5 = null;
        StringBuffer sbValueBeforeMD5 = new StringBuffer();

        try {
            md5 = MessageDigest.getInstance("MD5");

            long time = System.currentTimeMillis();
            long rand = 0;

            if (secure) {
                rand = secureRandom.nextLong();
            } else {
                rand = random.nextLong();
            }

            sbValueBeforeMD5.append(id);
            sbValueBeforeMD5.append(":");
            sbValueBeforeMD5.append(Long.toString(time));
            sbValueBeforeMD5.append(":");
            sbValueBeforeMD5.append(Long.toString(rand));

            this.valueBeforeMD5 = sbValueBeforeMD5.toString();
            md5.update(this.valueBeforeMD5.getBytes());

            byte[] array = md5.digest();
            StringBuffer sb = new StringBuffer();
            for (int j = 0; j < array.length; ++j) {
                int b = array[j] & 0xFF;
                if (b < 0x10)
                    sb.append('0');
                sb.append(Integer.toHexString(b));
            }
            this.valueAfterMD5 = sb.toString();
        } catch (NoSuchAlgorithmException e) {
            logger.debug("Error:" + e);
        } catch (Exception e) {
            logger.debug("Error:" + e);
        }
    }

    /**
     * Convert to the standard format for GUID (Useful for SQL Server
     * UniqueIdentifiers, etc). Example: C2FEEEAC-CFCD-11D1-8B05-00600806D9B6
     */
    public String toString() {
        String raw = this.valueAfterMD5.toUpperCase();
        StringBuffer sb = new StringBuffer();
        sb.append(raw.substring(0, 8));
        sb.append("-");
        sb.append(raw.substring(8, 12));
        sb.append("-");
        sb.append(raw.substring(12, 16));
        sb.append("-");
        sb.append(raw.substring(16, 20));
        sb.append("-");
        sb.append(raw.substring(20));
        return sb.toString();
    }

    /**
	 * Generate password
     */
    public String generateSecureString() {
        String raw = this.valueAfterMD5.toUpperCase();
        StringBuffer sb = new StringBuffer();
        sb.append(raw.substring(0, 10));
        return sb.toString();
    }

    /**
	 * Generate password
     */
    public static String generateRandomKey() {
    	return (new RandomHelper(true)).generateSecureString();
    }    
    
    /**
     * 
     * @return
     */
    public static String getGUID() {
        return (new RandomHelper(true)).toString();
    }

    public static void main(String[] args) {
        //System.out.print(RandomHelper.getGUID());
    	
    	System.out.println(RandomHelper.generateRandomKey());
    }
}
